Lighting installation comprising a light source with adjustable light-intensity



July 5, 1955 J. c. MOERKENS 2,712,617 LIGHTING INSTALLATION COMPRISING A LIGHT SOURCE WITH ADJUSTABLE LIGHT-INTENSITY Filed March 13, 1955 /o a 10 a 5 1/ m t: 6 b a 6 E 2 .oYoMM'It'O' M INVENTOR JOZEF CORNELIS MOER KENS BY %W%7/ AGENT United States Patent LIGHTING INSTALLATEON COMPRISING A LIGHT SOURCE WITH ADJUSTABLE LIGHT-IN'I'ENSI'I'Y Jozef Cornelis Moerkens, Eindhoven, Netherlands, as-

signor to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application hlarch 13, B53, Serial No. 342,244

Claims priority, application Netherlands April 5, 1952 7 Claims. (Cl. 315-99) For the lighting of trains, aircraft, vessels, buses, bedrooms and the like, light sources are frequently required, of which the light-intensity is adjustable from full operating value to a comparatively small value, or conversely.

The present invention relates to lighting installations having an adjustable light-intensity.

According to the invention, the light source is a lowpressure arc-discharge tube, preferably a fluorescent lamp, which comprises two thermionic electrodes heated from without and of a resistance such that a local discharge between the extremities of each thermionic electrode occurs during heating, the tube having a length such that it can ignite only with heated thermionic electrodes, across which a local discharge occurs, at a potential which does not exceed the supply voltage, the thermionic electrodes being included in a circuit comprising two windings of a choke coil and a capacitor, which windings counteract one another in case of series-connection, one winding being connected in series with the tube and the other, in series with the capacitor, being connected parallel to the tube. Furthermore, provision is made of a manually-operated switch connecting, at one of its positions, those extremities of the thermionic electrodes which are adjacent the source of supply.

In this case the numbers of turns of the windings on the choke may be substantially the same, it being possible for the windings to be provided above one another on the same core of the choke.

The tube preferably has a length of 70 cms. at the most with an inner diameter of about 35 mms.

According to a particular feature of the invention, the capacitive reactance of the capacitor at the operating frequency is smaller, and preferably about smaller, than the value: supply voltage/normal operating current of the tube.

According to a further feature of the invention, the inductive reactance of each winding of the choke at the operating frequency and with passage of a current equal to the normal operating current of the tube flowing through the winding concerned, is equal to a twofold to fourfold of the value: tube voltage/tube current in normal operation.

According to a particular feature of the invention, the installation may comprise its own generator without speed regulator.

In order that the invention may be readily carried into eifect, it will now be described more fully with reference to the accompanying drawing, given by way of example.

Fig. 1 shows the diagram of a lighting installation for railway waggons and Figs. 2 and 3 are side-views at right angles to one another, of the choke used in such an installation.

In Fig. 1, reference numeral 1 indicates a generator of about 110 volts, 400 C./S., which serves for the supply of fluorescent lamps 2. Said lamps are low-pressure mercury-vapour arc-discharge lamps containing, in addition to mercury, a filling or igniting gas, for example argon at a pressure of some millimetres, and of which VA-power to be supplied by the generator.

ice

either the wall or a fluorescent substance provided thereon causes the ultraviolet rays produced in the mercury discharge to be converted into visible rays. The lamps are connected to supply lines 3, 4, which may be connected by way of a main switch 5 to the generator.

The lamps comprise thermionic electrodes 6, 7. One extremity of each thermionic electrode e is connected, by way of a choke winding 8, to the supply line 3 and one extremity of each thermionic electrode 7 is connected to the supply line 4. Some extremities of the thermionic electrodes may be interconnected by a manually-operated switch 9. The other extremities of the thermionic electrodes 6, 7 are interconnected without the interposition of a switch by way of a second choke winding 10 and a capacitor 11. The sequence of winding 10 and capacitor 1 is not essential.

The lamps have the shape of straight tubes having a length of about crns. and an inner diameter of about 35 rnms, consuming a lamp current, about 420 m. amps. at a lamp voltage of about 36 volts. Said lamps ignite at a voltage not higher than the voltage of the generator, if the thermionic electrodes are heated to emission temperature and a discharge across the extremities of each thermionic electrode occurs.

The windings 8 and it of the choke are wound or connected so as to counteract one another when traversed by a non-tapped series-current. The numbers of turns of the two windings on the choke are preferably the same.

The operation of the installation is the following.

When the main switch 5 is closed and the manuallyoperated switch 9 is open, a series-current of about 475 milliamps. traverses the winding 8, the thermionic electrode 6, the winding it the capacitor 11 and the thermionic electrode 7. If the windings 8 and ill have the same number of turns, they neutralize one another, so that the series-current is substantially determined only by the reactance of capacitor 11. The capacitor is so proportioned that the series-current is greater than the normal operating current of 420 milliamps. of the lamps and has, for example, the said value of 475 milliamps.

The thermionic electrodes are heated to emission tem perature by the series-current, a local discharge occurring across the extremities of each thermionic electrode and causing ignition of the lamp. To ensure ignition, the lamp is required to be shorter than cms.

The ignited lamp represents the normal operating condition. Since the burning lamp is connected parallel to the series-combination of winding 10 and capacitor 11, three different currents occur, the lamp itself, winding 10 and capacitor 11, and winding 8 being traversed by a current of about 420 milliamps, a current of about 430 milliamps, and a current of about milliarnps. respectively. The last-mentioned current is materially smaller than the current of the lamp. This implies that the work factor of the inductively stabilised lamp is increased by capacitor 11 and this is highly desirable in view of the it is to be noted that, during heating up the incandescent electrodes, a greater current is absorbed, but the period of heating is so short, for example less than 1 second, that any appreciable overload of the generator cannot occur.

If the manually-operated switch 9 is now closed or if the lamp is put into use with this switch closed, the following situation occurs. The winding 8 is directly connected, by way of the manually-operated switch 9, to the supply voltage; a voltage is induced in the winding 10 by way of transformation, which voltage causes, by way of capacitor 11, the flow of a current of about 460 milliamps. through the thermionic electrodes, thus causing again local discharges across these electrodes. The lamp now cannot ignite, since it is short-circuited by the manually-operated switch 9. However, the local disof about 120 milliarnps. only being taken up from the vided above one another on a central core 12 of the iron circuit'of the shell type shown in Pig. 2. The windings 8 and 10 each have 465 turns. The central core 12 has a width of 12.8 mms. with a height of stack of mms. and comprises an air-gap 13 having an axial length of 0.8 mm. The windings 8 and 10 each have an impedance of 250 ohms at a current of 420 milliarnps, 400 C./S. A local discharge occurs across the thermionic electrodes when applying to them a voltage higher than 11 volts, which corresponds to an electrode resistance of 34 ohms at emission temperature.

As mentioned before, the lamps are stabilized inductively. This affords the advantage that the generator needs no speed regulator, since an increase in the voltage of the generator involves an increase in the frequency of the current generated and hence an increase in the inductive series-resistance of the lamps, so that variations in the voltage of the generator have little influence only.

It is evident that the lighting installation according to the invention is suitable not only for mobile installations comprising their own generator and a plurality of lamps, but also for connection of a single lamp to the alternating-current mains, for example, for the adjustable lighting of bedrooms. 7

What I claim is:

1. An adjustable-intensity lighting installation comprising a low-pressure arc-discharge tube having a pair of thermionic electrodes, each of said electrodes having two' terminals, a source of supply voltage, a pair of choke coils each having a winding, a'capacitor, one terminal of one of said electrodes being connected to one side of said source, one of said'windings connecting the other side of said source to one terminal of the other of said electrodes, the other of said windings being connected to the other terminal of said'other electrode, said windings being arranged to counteract'one another, said capacitor being connected in series with said other winding and the other terminal of said one electrode, 'and a switch interconnecting said one terminal of said one electrodeand said one terminal of said other electrode.

2. A lighting installation as claimed in claim 1 in which the choke coils are constituted by separate wind ings on the core of a transformer each having the same number of turns, and in which the switch is a manuallyoperated on-ofi switch.

3. An adjustable-intensity lighting installation comprising a low-pressure arc-discharge tube having a pair of thermionic electrodes, said electrodes each having a resistance at which a local discharge occurs thereat when heated, each of said electrodes having two terminals, a

source of supply voltage, said tube having a length at which ignition occurs at said supply voltage only when the thermionic electrodes thereof are heated, a transformer having two windings, a capacitor, one terminal of one of said electrodes being connected to one side of said source, one winding of said transformer connecting the other side of said source to one terminal of the other of 7 said electrodes, the other of said windings being connected to the other terminal of said other electrode, said windings being arranged to counteract one another, said capacitor being connected in series with said other winding and the other terminal of said one electrode, and a manually-operated switch interconnecting said one terminal of said. one electrode and said one terminal of said other electrode.

4. A lighting installation as claimed in claim 3' in which the tube has a length of not more than about cms. and an inner diameter of about 35 mms.

5. An adjustable-intensity lighting installation comprising a low-pressure arc-discharge tube having a pair of thermionic electrodes and adapted to operate at a normal tube current and tube voltage, each of said electrodes having two terminals, a source of supply voltage at a given frequency, a transformer having two windings of the same number of turns, a capacitor, one terminal of one of said electrodes being connected to one side of said source, one winding of said transformer connecting the other side of said source to one terminal of the other of said electrodes, the other of said windings being connected to the other terminal of said other electrode, said windings being arranged to counteract one another, said capacitor being connected in series with said other winding and the other terminal of said one electrode, and a manuallyoperated on-ofi switch interconnecting said one terminal of said one electrode and said one terminal of said other electrode.

6. A lighting-installation as claimed in claim 5 in which the capacitor has a value of capacitance at which it exhibits a reactance at the given frequency which is about 10% smaller than the quotient of the supply voltage by normal tube current. a

.7. A lighting installation as claimed in claim 5 in which the reactance of each winding at the given frequency when traversed by the normal tube current is equal to about two to four times the quotient of tubevoltage by normal tube current.

References Cited in the file of this patent UNITED STATES PATENTS 

